Frenzy followed the basic paradigm set by Berzerk: you are in a maze full of hostile robots who are shooting at you. The goal of the game is to survive as long as possible and score points by killing robots and travelling from room to room. The game has no end other than the player losing all of his or her lives.
You have a gun, so you can shoot back, and the robots are fortunately not that bright, and so can often be tricked into shooting each other. If you linger too long in a room, however, a bouncing smiley face, "Evil Otto", appears, and relentlessly chases you. Evil Otto will happily destroy any robots in his way, and can move through walls.
Differences from Berzerk
In Berzerk, the walls are all electrified and can kill you if you touched one of them. In Frenzy, some of the walls of the maze are composed of "dots" which can be shot. This opens up strategies such as blasting a hole in the side of a room to escape when in trouble. The solid walls, on the other hand, now reflect shots. You can trick robots into killing themselves by standing on the opposite side of a reflective wall and letting them shoot themselves. The only wall that simply absorbs shots harmlessly as in the original is the closed door that appears behind you when you enter a new room.
Neither type of wall is electrified, and so you can touch them without dying. On the other hand, you also usually can't kill robots by tricking them into walking into the now-harmless walls. In addition, you can no longer die by touching the robots or their explosions. Only their shots can kill you (though the blast radius from an exploding robot can kill you). There are two types of robots: skeletons and tanks. The two types have identical AI, but the skeletons are more difficult to shoot from above or below (because they're so thin).
In Berzerk, Evil Otto was unkillable and unstoppable. In Frenzy, shooting him once changes him from a smiley face to a "neutral" face, and another shot converts him to a "frowny" face. Another shot kills him. However, each time you kill Evil Otto makes him a little bit faster the next time he appears, which is usually immediately.
Every four mazes features interactive, decorative elements that were not present in Berzerk. In one room is a huge statue of Evil Otto, for example. Each one has a specific effect on gameplay for that one room. The order is: Big Otto, Power Plant, Central Computer, and Robot Factory. The Power Plant and the Central Computer are surrounded by walls made entirely of "dots", while Big Otto and the Robot Factory are surrounded by reflective walls with only one breakable "dot" in the corner, making them more difficult to hit.
In the Power Plant room (see screenshot), shooting the power plant once will disable it, and all robots in the room will stop moving. In the Central Computer room, shooting the computer will cause all the robots to start moving and firing erratically. While they're in such a state, the walls can kill them. The Robot Factory will continue to spit out additional robots while you're in the stage, taunting you as it does so. Shooting the factory has no effect (however, in the Coleco port, shooting the factory will disable it and stop the endless stream of robots).
In the Big Otto room, if you kill Evil Otto, not only does he immediately respawn as usual, but the Big Otto sends four more Ottos at you, all moving at top speed. Like the Robot Factory, shooting Big Otto has no effect. Big Otto starts out with closed eyes and a neutral expression, but his expression changes to one of rage, with glowing red eyes and a frowning mouth, when you kill Evil Otto. He also smiles when you die, though his eyes remain the same as before, either closed or open.
Finally, the robots are nowhere near as chatty. They only speak in a few specific situations. They say "Robot attack!" when Evil Otto appears, "Charge attack shoot kill destroy" when you kill Otto and he respawns, "The humanoid must not destroy the robot" when entering the Big Otto room, "The humanoid..." when shooting the Central Computer, and randomly alternates between "A robot must get the humanoid" and "A robot, not a chicken" when the Robot Factory dispenses a new robot. The constant background chatter of the original game is gone.
Frenzy was a less popular game than Berzerk, possibly because it was even more difficult. Frenzy was ported to the ColecoVision home video game console and the Sinclair ZX Spectrum home computer in 1983.